This is a point of confusion I still have with the simulation argument: Upon learning that we are in an ancestor simulation, should we be any less surprised? It would be odd for a future civilization to dedicate a large fraction of their computational resources towards simulating early 21st century humans instead of happy transhuman living in base reality; shouldn't we therefore be equally perplexed that we aren't transhumans?
I guess the question boils down to the choice of reference classes, so what makes the reference class "early 21st century humans" so special? Why not widen the reference class to include all conscious minds, or narrow it down to the exact quantum state of a brain?
Furthermore, if you're convinced by the simulation argument, why not believe that you're a Boltzmann brain instead using the same line of argument?
The problem with Dust theory is that it assumes that conscious states supervene on brain states instantaneously. There is no evidence for that. We should not be fooled by the "specious present". We seem to be conscious moment-by-moment, but the "moments" in question are rather coarse-grained, corresponding to the specious present of 0.025-0.25 second or so. It's quite compatible with the phenomenology that it requires thousands or millions of neural events or processing steps to achieve a subjective "instant" of consciousness. Which would mean you can't salami-slice someone's stream-of-consciousness too much without it vanishing, and also mean that spontaneously occurring Boltzman-consciousnesses are incredibly unlikely (because you would need a string of states to arise that are "as if" causally connected). Additionally, the idea of computational supervening on instantaneous snapshots of physical activity, irrespective of causal connection and temporal sequence, doesn't make much sense as a theory of computation. What is the difference between a computational state and any old state, if not the fact that is part of a computation, that is, a sequence of states.